Trends & Patterns

2016: How does Delhi’s air pollution this winter compare with last year?Air pollution this winter season is worse than it was last winter. In their report of Jan 2016, The Environment Pollution (Prevention & Control) Authority for the National Capital Region (EPCA) note a higher number of days reported in the “severe” category of the National Air Quality index, which is four times the safe standard for the months of November and December 2015 than those of 2014. In addition, December 2014 had at least 3% days falling in the “good” or “satisfactory” categories, and December 2015 had none. The Center for Science and Environment report 11 “smog episodes” (three consecutive days of air pollution measuring in the severe category) in this year’s winter.

What are the longer-term trends of air pollution in India?The influential Environmental Performance Index (EPI) released from Yale and Columbia universities, points to a much longer-term trend of air quality decline in the country. The 2014 EPI reports that India has seen a 100% decline in the EPI air quality scores over the past decade.

An EPCA report on the National Capital Region of Delhi provided data corroborating this trend of decline in air quality in their 2014 report:

From 2002-2012 particulate matter in Delhi has increased by 75% and numbers of vehicles on the roads have increased 97%, contributing enormously to pollution load and direct exposure to toxic fume.

In the winter of 2013- 2014 Delhi’s air pollution increased to dangerous levels. PM 2.5 particles have remained 2-3 times the national standard and have reached 8-10 times the standards in high smog episodes.

India’s Ministry of Earth Sciences reports that the frequency of extreme pollution events is on the increase. With PM10 levels in January 2014 the highest so far.

Seasons in DelhiCooler Months: Particulate matter air pollution is generally worse in the winter during the “inversion” when cooler air temperatures trap smog closer to the ground.

The graph below produced by the EPCA and based on data from the Delhi Pollution Control Committee shows daily PM 2.5 measures for the winter 2013-2014 from Oct.- Jan. 2014)

Source: Based on real-time data from the website of Delhi Pollution Control Committee. (“EPCA Report (February 2014) Report on Priority Measures to Reduce Air Pollution and Protect Public Health”)

Warmer months: According to the Center for Science and Environment, ground-level ozone peaked to dangerous levels during the heat-wave of June 2014. Ground-level ozone is formed when oxides of nitrogen (NOX) and other volatile gases oxides are exposed to each other in sunlight. CSE experts say warm temperatures and extreme heat threaten to increase the frequency of days with unhealthy levels of ozone. (For more information on this, visit CSEindia then follow the link to Press: CSE in news)

Daily patterns in DelhiAir pollution in Delhi often peaks around midnight. On hazardous days, the mornings are often worse and the pollution seems to dissipate as the day progresses. To check out the daily ebbs and flows of air pollution, you can access the public information provided by the government-run Delhi Pollution Control Committee. Click on the location you want and then the pollutant (for ex. PM 2.5) and then click “line graph”

Holidays: DiwaliIf you are curious about the pollution caused by fireworks during the Diwali holiday, see the following analysis by the Center for Science and Environment (CSE), a public interest group. CSE used data provided by the Central Pollution Control Board from Diwali 2012, looking at real-time measures from the time period of 7pm to 1am, the time frame when most fireworks are set off. Some key Findings:

What about Diwali 2014? CSE has a new piece on the measurements of pollution from this year’s Diwali (high) and also the need for longer-term management strategies: Diwali Pollution Management Needs Rethink